Corrosion inhibition



A g- 1965 E. M. GREELEY ETAL 3,200,604

CORROSION INHIBITION Filed Jan. 29, 1962 oooooooo oooooooooo o o o o o o o o o o 2s 22 49 26 0 Q1: H 75 EDWARD u g n gg v r RANDOLPH N. STENEFiSON.

ATTORNEY.

United States Patent 3,200,604 CGRRUSION INITION Edward M. Greeley, Syracuse, and Randolph N. Stenerson, De Witt, N31, assignors to (Carrier (Iorporation, Syracuse, N .Y., a corporation of Delaware Filed Jan. 29, 1962, Ser. No. 169,508 13 Claims. (Cl. 62-85) This invention relates to absorption refrigeration machinery and more particularly, it relates to the inhibition of corrosion in an absorption refrigeration machine of the type which is subject to corrosion of metal surfaces of the machine due to corrosion reactions which take place within the machine.

The advantages of using absorption refrigeration equipment in certain applications have been well appreciated for many years. Since absorption refrigeration machines can be broadly considered as heat operated equipment, it will be readily appreciated that they can be conveniently used in many applications where a source of steam or hot water, or combustible gas, is readily available to operate the equipment.

However, one of the problems which confronts the designer of absorption refrigeration equipment has been that of combating the corrosion, particularly of iron containing metal surfaces, in the interior of an absorption refrigeration machine. Large size absorption refrigeration machines commonly use an aqueous solution of a salt such as lithium bromide as the absorbent medium and, generally, use water as the refrigerant. However, lithium bromide solutions tend to promote corrosion of iron containing metal surfaces, particularly at high temperatures and in the presence of oxygen. Since a typical absorber pressure may be on the order of only of an atmosphere, ambient air, containing oxygen, tends to leak into the absorber at joints and other places. Consequently, even with an efficient purge unit connected to such a machine, there is frequently oxygen present in its interior to cause certain types of corrosion. In some cases, corrosion of a typical absorption refrigeration machine may be so severe as to render the machine completely inoperative in a period of only a relatively short time.

Furthermore, a trend in absorption refrigeration equipment has been toward larger size machines and toward the utilization of higher temperature heat sources in order to obtain maximum capacity from a minimum physical size. It has been found that corrosion is greatly accelerated in higher temperature machines therefore making a suitable solution to the corrosion problem a necessity in such machines.

In addition, in some applications it is highly desirable to use what is known as a direct fired absorption refrigeration machine wherein the heat of a combustible fuel,

such as gas, is directly used to fire the generator of the r absorption machine. In this application, it is extremely difficult to control or limit the formation of hot spots which have temperatures in localized areas very much greater than the average effective temperature in the generator. These hot spots, therefore, tend to become centers for localized highly accelerated corrosion which tend to cause rapid failure of the refrigeration equip ment. For this reason, direct fired absorption refrigeration equipment has been limited to relatively low temperature machines in order to avoid the formation of high temperature hot spots.

The mechanism of corrosion in an absorption refrigeration machine is complicated by the fact that a number of different reactions may take place in a single machine and by the fact that typical absorption refrigeration equipment employs heat exchange tubes which are generally made of copper or one of its alloys. The

,664 less ICC copper may be oxidized to form cuprous oxide, which in turn may be further oxidized by oxygen from air leakage into the system to form an insoluble cupric oxide sludge. This process is undesirable not only because it removes copper from the heat exchange tubes causing them to eventually fail, but also because the insoluble sludge which is formed may foul pump bearings, pump seals or other parts of the refrigeration equipment. In addition, cuprous oxide may react with iron containing metal surfaces in the machine to form an insoluble oxide of iron, while plating out the copper on the iron surface, thereby corroding the iron and structurally weakening the refrigeration machine.

Another form of corrosion which may take place even in the absence of oxygen is frequently observed. Iron containing metal surfaces give up electrons to hydrogen ions provided by the water in the absorbent solution, which results in iron ions going into solution and hydrogen gas being produced. In this case, the hydrogen gas interferes with proper operation of the absorption machine by blanketing the absorber tubes with gas. The hydrogen gas also forms a barrier layer over the absorbent solution and prevents absorption of refrigerant. This materially reduces the rate at which refrigerant vapor is absorbed by the absorbent solution, lessening the refrigeration capacity of the machine. Also, due to lessened absorption of refrigerant vapor, the absorbent solution is likely to crystallize, both because of super cooling in the absorber and because of over-concentration in the generator. Furthermore, the loss of iron from the iron containing metal surfaces by this electrochemical reaction represents highly undesirable corrosion, which may cause structural failure of the part being attacked.

One of the approaches to solving corrosion in an absorption refrigeration machine has been to add various corrosion inhibitors to the absorbent solution. In lithium bromide solutions, for example, it is frequent practice to render the solution alkaline by the addition of lithium hydroxide. By adding the proper amount of lithium hydroxide to a lithium bromid'e solution, a marked reduction in the rate of corrosion may be achieved. Rendering the absorbent solution alkaline, however, merely reduces the rate of corrosion, but does not satisfactorily prevent corrosion from taking place particularly at high temperature.

The size and cost of an absorption refrigeration machine is directly related to the temperature at which the generator may be operated, and it is desirable to operate the generator at as high a temperature as possible in order to obtain maximum capacity from a given size machine. Consequently, various other inhibitors such as chromate, nitrate and molybdate compounds have been tried in addition to lithium hydroxide in order to reduce the corrosion rate in absorption refrigeration machines. These inhibitors have proved fairly satisfactory at temperatures below 250 F., but have proved largely ineffective at high temperatures, particularly where oxygen has been present in the machine. Since steam temperatures well in excess of 250 are commonly available from desired steam sources and because direct fired absorption refrigeration machines are likely to have localized hot spots in various regions of the generator in excess of this temperature, these inhibitors have not proved wholly satisfactory in high temperature commercial absorption refrigeration machines.

Accordingly, it is an object of this invention to provide an absorption refrigeration machine which is capable of operating at relatively high temperatures.

It is a further object of this invention to provide an effective corrosion inhibitor and corrosion inhibited parts to enable an absorption refrigeration machine to be used at relatively high temperatures.

It is a still further object of this invention to provide a corrosion resistant alloy.

It is a still further object of this invention to provide a method of forming a corrosion inhibitor and a corrosion inhibiting coating on metal surfaces within an absorption refrigeration machine which are subject to corrosion during operation of the machine.

These and other objects of this invention are achieved in a preferred embodiment thereof by providing an absorption refrigeration machine utilizing an absorbent solution, such as lithium bromide and Water with a suitable antimonial material in the absorbent solution, so that metal surfaces, such as steel, within the machine, which are subject to corrosion when in contact with the absorbent solution will develop a corrosion inhibiting antimonial coating thereon. It has been discovered, for example, that when the oxides of antimony or lithium antimonite or lithium antimonate are dissolved in a lithium bromide solution containing lithium hydroxide there is formed on the surface of iron containing metal parts in contact with the solution, a highly tenacious, ductile, corrosion resistant, antimonial coating which resists corrosion at temperatures in excess of 390 F.

It has also been discovered that when an iron containing metal part which has been inhibited by exposure of a surface thereof with the previously mentioned compounds of antimony and lithium hydroxide and subsequently placed in a solution of lithium bromide and lithium hydroxide together with uninhibited iron containing parts, that the uninhibited iron containing parts have deposited on their surface a corrosion inhibiting, antimonial coating similar to that formed on the inhibited metal part. Consequently, an absorpton refrigeration machine may be suitably inhibited by precoating certain parts thereof which are in contact with the absorbent solution with an antimonial coating or by alloying or incorporating antimony ietal in such parts, because of the unexpected property of the inhibitor in migrating from the inhibited parts to uninhibited parts in contact with the solution. In addition, it has also been discovered that an absorption refrigeration machine containing an absorbent solution such as lithium bromide having lithium hydroxide in it may be suitably inhibited by merely placing a quantity of antimony metal into the absorption refrigeration machine at a point where it may be contacted by the absorbent solution.

The inhibitor described has greatly superior corrosion inhibiting properties compared with known inhibitors when used under comparable conditions of high temperature and in the presence of oxygen. For example, satisfactory corrosion inhibition of iron containing metal surfaces has been observed to exist at relatively high temperatures even in the presence of oxygen by utilizing the inhibitor and method described.

Other objects of this invention will become apparent by reference to the following specification and attached drawmg:

The figure is a diagrammatic cross-sectional view through an absorption refrigeration machine having metal surfaces inhibited in accordance with this invention.

Referring particularly to the drawing, there is shown a typical absorption refri eration machine comprising an absorber section within a shell Ill. A plurality of heat exchange tubes 12 are provided within the absorber section. A purge line 13 leads from a suitable region of the absorber and serves to conduct noncondensible gases therefrom to a suitable purge unit 76. A spray header 14 is located above the absorber section.

Also disposed in shell 11 is an evaporator section 15 comprising a pan-like member 16 within which is disposed a plurality of heat exchange tubes 17. A spray header 18 is located above heat exchange tubes 17 for distributing refrigerant thereover. A plurality of eliminators 19 are provided to prevent entrained liquid refrigerant particles being carried from evaporator section 15 to absorber section 10. Evaporator section 15 is in open communication with absorber section lit through eliminators 19.

In operation, a suitable refrigerant is sprayed over tubes 17 in evaporator section 15 and a suitable absorbent solution is sprayed over tubes 12 in absorber section It). Consequently, refrigerant is vaporized in evaporator section 15 and passes through the eliminators into absorber section it where the refrigerant vapor is absorbed by the absorbent solution. The vaporization of the refrigerant in evaporator section 15 extracts heat from the fluid passing through heat exchange tubes 17 and this heat is carried with the vapor into absorber section it where it is given up to a cooling fluid passing through heat exchange tubes 12. Thus, the evaporation of refrigerant in evaporator section 15 produces a cooling or refrigeration effect on the fluid passing through heat exchange tubes 17.

Line 21 is connected to pump 22 and serves to circulate absorbent solution of intermediate strength accumulated in the lower portion of absorber section It} through line 2-3 to spray header 14 in order to recirculate absorbent solution in the absorber. A line 24 leads from a lower portion of absorber section 1% containing weak solution and pump 25 serves to pass the weak solution through line 26 and solution heat exchanger 27 through line 23 to generator section 30.

As used herein, the term strong solution refers to an absorbent solution strong in absorbing power and the term weak solution refers to absorbent solution weak in absorbing power. The term intermediate strength solution refers to a solution having a concentration intermediate that of strong solution and weak solution.

A suitable absorbent for a refrigeration system of the type described comprises a hygroscopic aqueous salt solution such as lithium bromide and water. The concentration of the strong solution leaving the generator may be about 65%. A suitable refrigerant is water.

The absorption of refrigerant vapor by absorbent solution in absorber section ltt dilutes the absorbent solution and diminishes the refrigerant supply. In order to maintain the refrigeration machine in operation, it is necessary to concentrate this week solution by separating it from the absorbed refrigerant. For this purpose, a generator section 30 and a condenser section 32 are provided.

Generator section 30 is located in shell 34 and comprises a plurality of heat exchange tubes 31 for passing steam or other heating fluid. Also located within shell 34 is condenser section 32 comprising a pan-like member 35 within which is disposed a plurality of heat exchange tubes 33 for passing cooling water. Eliminators 36 are provided to prevent strong solution from being entrained in refrigerant vapor passed from generator section 3%) to condenser section 32.

A line 37 leads from pan-like member 35 to evaporator section 15 and serves to return condensed refrigerant from the condenser section to the evaporator section. Line 38 extends from generator section 30 through solution heat exchanger'27 to absorber section 10 and serves to return reiatively hot, strong absorbent solution from the generator section to the absorber section while passing it in heat exchange relation with relatively cool, weak solution being forwarded to the generator for concentration thereof.

A bypass line 39 and bypass valve 40 having a suitable actuator mechanism may be provided for capacity control of the refrigeration system. Reference is made to Leonard application Serial No. 2,203, filed January 13, 1960, now Patent No. 3,054,272, for a complete description of the operation of an absorption refrigeration machine including the operation of bypass line 39 and bypass valve 4% A steam inlet line 41 and outlet line 42 having suitable steam trap 43 is provided to admit steam to heat exchange tubes 31 in order to boil off refrigerant vapor from weak solution supplied to the generator, in order to concentrate the weak solution. It will be understood that the vaporized refrigerant passes through eliminators 36 and is condensed in condenser 32. A cooling water inlet line 44 is connected to heat exchange tubes 12 in absorber section from which the cooling water passes through line 45 to heat exchange tubes 33 in the condenser section. The cooling water is then discharged through line 46 and appropriate bypass line and valve 47 may be provided to bypass cooling water around the condenser section, if desired. The cooling water serves to remove the heat of dilution and condensation from the absorbent solution in absorber section 10 and serves to remove the heat of vaporization to condense refrigerant vapor in condenser section 32.

A suitable recirculation line 48 and recirculation pump 49 pass refrigerant from pan 16 of the evaporator section through line St to spray header 18 so that refrigerant may be sprayed over heat exchange tubes 17 to wet them and aid in evaporation of the refrigerant and cooling of heat exchange tubes 17. Lines 52 and 53 are provided to conduct a heat exchange fluid, such as water, through heat exchange tubes 17 to cool the fluid by the resulting heat exchange with the cooled refrigerant in evaporator 15. This cooled heat exchange fluid is then passed to suitable remotely located heat exchangers to provide cooling in the desired areas.

Tubes 12 and 31 as well as tubes 17 and 33 are typically composed -of copper or a copper containing alloy, such as cupro nickel. Shells 11 and 34, as well as the tube sheets into which the various heat exchange tubes are secured, and pans 35 and 16 are typically composed of a ferrous or iron containing alloy such as steel. Heat exchanger 27 is commonly a steel shell having tubes composed of steel therein. The temperature in generator 30 and line 38 under high refrigeration load operating conditions may at times exceed 250-300 F. due to steam or hot water passed through lines 41 and 42. It is apparent, therefore, that corrosion may take place in generator section 39 or heat exchanger 2'7, or in line 38, which is frequently a steel tube, as well as in other parts of the refrigeration system because of the high temperatures to which these parts are subjected. Furthermore, generator 30 may be of the direct fired type wherein heat exchange tubes 31 are exposed directly to a high temperature gas flame on their interior, in which corrosion of these tubes may be greatly accelerated In order to reduce the rate of corrosion in an absorption machine of the type described, which utilizes an aqueous solution of lithium bromide as an absorbent medium, it is desirable to render the solution alkaline by adding a quantity of lithium hydroxide. Lithium hydroxide may be desirably added to the absorbent solution to the extent of from about 0.2 gram to about 4.0 grams of lithium hydroxide per kilogram of lithium bromide salt. A typical 54% absorbent solution of the type described may preferably be rendered thereby approximately .1 normal in order to reduce the corrosion rate. The actual concentration of such a solution during operation of the machine is typically greater than 54%, but this concentration represents a suitable solution for initial charging of the machine and normality (gram equivalent weight per liter) may be related to this concentration by expressing the normality of the solution in terms of what it lsiVOld be if the solution were diluted or concentrated to As previously described, however, while the addition of lithium hydroxide to the absorbent solution reduces the rate of corrosion, the corrosion rate may still be excessive at desirable operating temperatures. It has been the absorbent solution, iron containing'metal surfaces and copper containing metal surfaces in contact with the ab- TABLE I Average Inhibitor Tempera- Weight ture, F. Change,

MDD

TABLE 11 Average Inhibitor Tempera- Weight ture, F. Change,

MDD

None (no LiOH) 225 -1o00 Sb (no LiOH) 225 -45. 5

TABLE III Average Inhibitor Tempera- Weight ture, F. Change,

MDD

, elated to 54% solution by the addition of lithium hydroxide. The solutions containing various inhibitors or no inhibitor in addition to the lithium hydroxide were boiled at the temperatures shown in Table I for a period of several weeks. The boiling took place in vessels which were exposed to atmospheric pressure and boiling was periodically interrupted so that the effect of an oxygen containing environment, which is known to produce serious corrosion, could be assessed. In each case the antimonial material was added in an amount substantially in excess of that amount which would dissolve in the aqueous lithium bromide, lithium hydroxide solution so that excess antimonial material was at all times present in a solid form in thetest vessel. The concentration of the lithium bromide in the solution was adjusted to obtain the boiling points indicated at atmospheric conditions. The steel samples were then removed from the solution, dried, and reweighed to determine what effect the inhibitor had in preventing corrosion of the steel. A weight change in milligrams per square decimeter of exposed surface per day was then computed for each of the samples and averaged to obtain the values shown in Table I.

It will be observed from Table I that when no additional inhibitor other than lithium hydroxide was added to this solution, that an average weight loss of one milligram per square decimeter per day was observed at 225 sample and is therefore an indication that the steel sample was corroding or losing weight. On the other hand, the weight gain shown when an antimonial material was added to the solution, represents a deposition on the surface of the metal sample of a coating which was found to contain antimony, which can be described as an antimonial coating.

Upon removing the steel samples from the solution, it was found that each of the steel samples in the inhibited solution had a bright surface coating which, under analysis, proved to contain a substantial quantity of antimony. Bending these samples showed that the surface coating did not tend to crack, thereby indicating that the coating formed was ductile and highly tenacious.

Furthermore, it will be noted from Table I that no weight loss was observed even at temperatures as high as 340 and in the presence of greatly more oxygen than could be tolerated in an ordinary absorption refrigeration machine. The weight gains appeared to increase with temperature indicating that more antimonial corrosion resistant material was formed on the surface of the steel samples at high temperatures than at low temperatures.

For purposes of comparison, Table II is given which shows the effect of similar tests performed in the presence of air in aqueous lithium bromide solutions with the omission of lithium hydroxide. It will be observed that extremely severe corrosion rates in excess of 1000 milligrams per square decimeter per day result when no lithium hydroxide is present in solution, but that by the mere addition of antimony metal to the solution, a very substantial reduction in corrosion rate is observed.

Table III tabulates tests conducted at high temperatures where only a small amount of air was present. The test vessels were sealed and in all cases the concentration of lithium bromide in the solution was approximately 65% and lithium hydroxide was added in an amount sufficient to render the solution 0.1 normal (related to 54% solution) which corresponds to a typical concentration in a generator of a high temperature absorption refrigeration machine. It will be observed from the table that very substantially smaller corrosion rates or actual weight gains were observed by the addition of the antimonial materials listed, even at temperatures as high as 390 F. compared to the relatively high corrosion rate where only lithium bromide and lithium hydroxide were present at a lower temperature of 300.

Besides the properties of ductility, tenacity and corrosion resistance which have been previously referred to, the antimonial coatings formed on the surface of the steel samples in the foregoing tests exhibited the unexpected property of migrating to uninhibited steel specimens. For example, various samples of the inhibited steel surfaces having an antimonial coating thereon from the previous tests were placed in an uninhibited solution of lithium bromide having a concentration of about 65%, which was rendered 0.1 normal related to 54% solution with lithium hydroxide. Other samples of uninhibited steel were also placed in the same solution and the solution boiled at atmospheric pressure in the presence of oxygen. It was found that not only did the inhibited steel samples fail to indicate corrosion on their surfaces, but that after a period of time some of the antimonial material from the inhibited steel specimens migrated to the surfaces of the uninhibited steel specimens and greatly reduced the expected rate of corrosion of the latter specimens.

This migration of inhibitor is a particularly desirable property in an absorption refrigeration machine since it indicated that, should the coating for any reason be removed on a surface in contact with the absorbent solution which is subject to corrosion, or in the case that the inhibitor becomes used up during operation of the machine, that some migration of the inhibitor will take place to protect uninhibited parts subject to corrosion. In ad- 8 dition, because the antimonial coating possesses the property of migrating to uninhibited parts, it is possible to precoat certain parts in an absorption refrigeration machine with a layer of the antimonial coating, and during operation of the machine, other parts subject to corrosion will be inhibited by migration of the antimonial coating to the uninhibited portions. Consequently, antimony metal or other antimonious material may be incorporated in or alloyed with metals used in the absorption refrigeration machine, as well as coated on them to provide the desired corrosion inhibition both on the surface of the parts themselves as well as other metal surfaces in the machine. It has also been observed that a corrosion inhibiting antimonial coating is formed on copper containing surfaces when copper containing metals are present in a similar lithium bromide and lithium hydroxide absorbent solution containing an antimonial material which is in contact with both the copper containing metal and ferrous metal surfaces such as steel.

In order to further test the effectiveness of the antimonial inhibitor described herein, a previously operating absorption refrigeration machine, of the type herein described, of approximately tons capacity was inspected and then antimonially inhibited and run with a 0.1 normal (related to 54% solution) aqueous solution of lithium bromide having lithium hydroxide therein. Lithium antimonite was completely dissolved in a water solution which was added to the absorbent solution to provide an initial concentration of 44 parts per million of the inhibitor in the absorbent solution. The machine was run for a period of four months and then torn down to examine the effect of the lithium antimonite on various parts-which were exposed to absorbent solution. It was found that an antimonial coating had formed on the various metal parts of the machine, such as the steel shell of the generator. Surprisingly, it was also found that the copper plating which is normally an incident of some forms of corrosion was no longer present on various metal surfaces upon which it had previously formed, and it appeared that the inhibitor had effectively reduced the rate of corrosion of the metal surfaces in contact with the absorbent solution. The inhibitor coating appeared to be present on brass, bronze, cupro nickel, and steel surfaces within the machine.

The mechanism of the corrosion inhibition herein described may possibly be explained by considering that a piece of antimony metal, antimonial material, or an otherwise antimonially inhibited part in an absorption refrigeration machine may react with lithium hydroxide in the lithium bromide solution forming lithium antimonite. The lithium antimonite may be further oxidized by oxygen present in the machine or react with lithium hydroxide to form lithium antimonate, which in turn reacts on the surface of the various metal parts in contact with the absorbent solution, providing an antimonial i.e. antimony containing coating. Consequently, the inhibitor, when added in this form, may serve to not only inhibit the metal parts of the machine by forming a coating on them, but may scavenge oxygen which is present in the machine which would otherwise cause corrosion of these parts.

In order to inhibit an absorption refrigeration machine in accordance with this invention, it is preferred to introduce an antimonial materal such as antimony, antimony trioxide, antimony pentoxide, antimony tetroxide, lithium antimonite, or lithium antimonate into the machine at a point at which it will contact absorbent solution. This may be done by either adding the antimonial material directly to the absorbent solution either in solid or dissolved liquid form, or it may be done by. precoating a part of the machine with the reaction product of an antimonial material and lithium hydroxide. Likewise, a part of the machine may be made of antimony metal or a quantity of antimony metal may be added to the machine in solid form at some convenient place, such as the purge unit, wherein it contacts absorbent solution. The antimonial material then dissolves in the absorbent solution and is carried by the solution to other portions of the machine in contact with the solution thereby forming the desired antimcnial coating on those parts.

Likewise, antimony metal may be incorporated into or alloyed with a part of the machine such as the heat exchange tubes, which can be, for example, an alloy of copper, nickel and antimony, or the tubes may have a coating of an antimonial material on their surface to provide the desired result. An alloy of copper and nickel containing less than about 2% antimony is satisfactory for this purpose.

The antimonial coatings or alloys described herein possess the unique and highly desirable advantage of being themselves corrosion resistant, while at the same time having the property of tending to inhibit those metal portions of the absorption refrigeration machine which are subject to corrosion by being in contact with absorbent solution. By the practice of this invention there is formed in the absorption refrigeration machine an antimonial coating or alloy which imparts superior corrosion resistant properties at relatively high temperatures even when substantial oxygen is present in the system to cause oxidation of the metal surfaces. Furthermore, in systems containing both copper and iron, both of these metals can be inhibited by the practice of this invention.

Various modifications and equivalents of the method and apparatus herein described, falling within the scope of this invention, will readily occur to those skilled in the art, and, therefore, the foregoing specific examples of this invention are given merely by way of illustration. Accordingly, it is foreseen that the invention may be otherwise embodied within the scope of the following claims. I

We claim:

1. An absorption refrigeration machine comprising an absorber, a generator, a condenser and an evaporator, an absorbent solution in said machine, at least a portion of said machine in contact with said solution being made of a metal subject to corrosion, means to pass said absorbent solution through said machine into contact with said metal, said absorbent solution including a hygroscopic salt of lithium, lithium hydroxide, and a corrosion inhibitor comprising an antimonial material.

2. An absorption refrigeration machine as defined in claim 1 wherein said corrosion inhibitor comprises antimonial material which is selected from the group consisting of antimony, the oxides of antimony, lithium antimonite and lithium antimonate.

3. An absorption refrigeration machine as defined in claim 2 wherein said salt of lithium comprises lithium bromide, and wherein said lithium hydroxide consists of between about .2 gram and about 4 grams per kilogram of lithium bromide.

4. A corrosion inhibited absorption refrigeration machine having a generator, a condenser, an absorber and an evaporator connected to provide refrigeration, an absorbent solution including lithium bromide having lithium hydroxide therein and at least one corrosion inhibited metal part in said absorption refrigeration machine which is adapted to be exposed to said absorbent solution, said metal part comprising an alloy of antimony.

5. An absorption refrigeration machine as defined in claim 4 wherein said metal part comprises a tube and said alloy comprises an alloy of at least the metals copper and antimony.

10 corrosion which is adapted to be exposed to said absorbent solution, said machine having a corrosion inhibitor therein comprising an antimonial material adapted to be contacted with said absorbent solution to inhibit the corrosion of said metal surface.

'7. The combination of an absorption refrigeration machine having a metal surface therein which is subject to contact with an absorbent solution, and an absorbent solution comprising lithium bromide, lithium hydroxide and a corrosion inhibitor comprising an antimonial material.

8. A combination as defined in claim 7 wherein said antimonial material comprises antimony metal.

9. A combination as defined in claim 7 wherein said antimonial material comprises an oxide of antimony.

10. A combination as defined in claim 7 wherein said antimonial material comprises lithium antimonate.

11. A method of forming a corrosion resistant coating on metal parts in an absorption refrigeration machine comprising an absorber section, an evaporator section, a generator section, a condenser section, and means interconnecting said sections to form an absorption refrigeration system including means to circulate an aqueous absorbent salt solution in said machine, at least a portion of said machine comprising a corrodible metal surface, which consists in the steps of introducing antimony meta-l into said absorbent solution and contacting said metal with the absorbent solution having antimony therein to provide a corrosion inhibiting coating on said metal surface.

12. In the art of absorption refrigeration, the method of operating an absorption refrigeration machine having a metal surface therein which is subject to corrosion, said machine comprising an evaporator section, an absorber section, a condenser section, a generator section, and means to circulate an aqueous absorbent solution therein, which consists in forming an antimonial, corrosion resisting, coating on said metal surface.

13. An absorption refrigeration machine having an absorbent solution therein and including a metal component having a surface which is subject to corrosion and is in contact with said absorbent solution, said absorption refrigeration machine having a corrosion inhibitor comprising antimony in said absorbent solution to inhibit corrosion of the surface of said metal part.

References Cited by the Examiner UNITED STATES PATENTS 1,719,762 7/29 Gollmar 23225 1,796,123 3/31 Samesreuther et al. 165-133 1,959,509 5/34 Tour 149 2,120,737 6/38 Domm l65-133 X 2,455,457 12/48 Whitfield et a1. -133 2,457,334 12/48 Widell 62-85 2,580,983 1/52 Widell 62-85 2,582,306 1/52 Zellhoefer et a1. 252-68 2,643,178 6/53 Wachter et al 25268 X 2,710,253 1/55 Willardson et a1. 75-149 2,755,170 7/56 Stubblefield 62-85 X 2,825,683 3/58 Lowenheim et al. 75149 X 2,864,731 12/58 Gurinsky et al 165133 X 2,867,550 1/59 Weber 75'149 X 2,900,222 8/59 Kahler et a1. 11797 X 3,004,919 10/61 Rush et al. 252-67 3,014,349 12/61 Leonard 62-476 X 3,065,609 11/62 West 6285 3,087,778 4/63 Negra et a1. 252-387 X 3,087,897 4/63 Stedt et a1. 25268 ROBERT A. OLEARY, Primary Examiner. 

1. AN ABSORPITON REFRIGERATION MACHINE COMPRISING AN ABSORBER, A GENERATOR, A CONDENSER AND AN EVAPORATOR, AN ABSORBENT SOLUTION IN SAID MACHINE, AT LEAST A PORTION OF SAID MACHINE IN CONTACT WITH SAID SOLUTION BEING MADE OF A METAL SUBJECT TO CORROSION, MEANS TO PASS SAID ABSORBENT SOLUTION THROUGH SAID MACHINE INTO CONTACT WITH SAID METAL, SAID ABSORBENT SOLUTION INCLUDING A HYGROSCOPIC SALT OF LITHIUM, LITHIUM HYDROXIDE, AND A CORROSION INHIBITOR COMPRISING AN ANTIMONIAL MATERIAL. 